There are three types of glare: direct, contrast and indirect. Direct glare occurs when there are bright light sources directly in the operator's field of view. Windows are often a source of direct glare, or one may experience the direct glare by looking straightly to the sun or a light bulb. Contrast glare is where one part of the vision area is much brighter than another. Usually it is caused by large differences in light levels within the visual field. For example, it may happen when there are two light sources illuminating a same general area, such as a study room, in that an area light such as the luminaire fitted on the ceiling is used for lighting the whole study room while a task light such as a desktop lamp is used for lighting a working area on the desk, thereby, large differences in light levels will be caused in the visual field. Moreover, indirect glare occurs when light from windows or overhead lighting is reflected off shiny surfaces in the field of view, such as terminal screens, desks and other office equipment, which is considered to be the most commonly experienced glare and is the one that causes most discomfort to human eye. One important fact must be remembered: glare is light—it is impossible to alter glare without altering the light entering through the glazing. Therefore, as the indirect glare viewed in the field of view is substantially a kind of secondary light originating from and reflected by a glassy surface of a reading material being viewed by a person, the glare troubling the person, being the reflection of the light shining on the reading material, is impossible to be avoided without changing his or her normal orientation to the reading material.
Indirect glare can be a significant problem, since it may be the cause of burred images, strenuous reading, low reading efficiency, and even severe eyestrain and headaches. Many researches had indicated that four out of five working professionals are troubled by some kinds of visual discomfort and have symptoms such as headache, eye fatigue or watering eye. Statistically, within a sample group of students, more than 55.9% of them specify that it is common for them to be troubled by eyestrain, watering eye, etc. while studying under the lighting of desk lamps.
For dealing with those visual discomfort problems caused by indirect glare, many anti-glare structures had been provided which can be divided into three types: structures with anti-glare reflective filter, structures with anti-glare reflective screen and structures with optical chopper.
For those anti-glare structures with anti-glare reflective filter, it is common to design a reflective filter at the lighting direction of a light source so that only light of vertical polarization is allowed to pass through the reflective filter while other light of parallel polarization is reflected for converting into vertical polarization, thereby, indirect glare can be reduced. Moreover, a diffusive film matching with the reflective filter is usually being designed in such anti-glare structures, by which light can be diffused uniformly before shining on the reflective filter so that even when a person is looking directly at such anti-glare structures, it can prevent the person from seeing and identifying the exact light source and thus the adverse effect of direct glare is reduced. However, since the use of such reflective filter will result a portion of light to be dissipate during the reflection, the light efficiency and the brightness of any luminaire using such anti-glare structures are reduced and thus may not be satisfactory.
For those anti-glare structures with anti-glare reflective screen, it is common to design a reflective screen surrounding a light source of a luminaire so that the reflective screen will reflect and direct the light of the light source to shine perpendicularly toward a desired working area on a desk, thereby, indirect glare can be reduced as light reflected from the glassy surface of the working area will not shine directly to human eyes. Moreover, a soft screen matching with the reflective screen is usually being designed in such anti-glare structures, by which light can be scattered even when a person is looking directly at such anti-glare structures, it can prevent the person from seeing and identifying the exact light source and thus the adverse effect of direct glare is reduced. However, it is disadvantageous in that: the use of such reflective screen will result in the luminaire to have smaller lighting area, not to mention that it is much more complicated to design and manufacture. In addition, any luminaire designed with such soft screen will have poor light efficiency inferior to those without.
For those anti-glare structures with optical chopper, it is common to design an optical chopper surrounding a light source of a luminaire for controlling the lighting direction of the light source, by which not only glare can be prevented, but also most light emitted from the light source can be used effectively and thus the efficiency of the light source is increased. However, it is disadvantageous in that: the use of such reflective screen will result in the luminaire to have smaller lighting area, not to mention that the overall light efficiency of the luminaire is adversely affected.
From the above description, it is noted that although those conventional anti-glare structures can function effectively in glare improvement, they are all suffered by problems of smaller lighting area and lower light efficiency.
There are several researches trying to develop an anti-glare structure with improved light efficiency and uniformity. One such research is a lighting device disclosed in U.S. Pub. No. 20060232976, entitled “Lighting Device With Integration Sheet”, as seen in FIG. 1. The lighting device of FIG. 1 comprises: a light source 21 having a luminous body 211 and a reflecting screen 212; and a sheet 22, being disposed at the light emitting end of the light source 21, each comprising a plurality of light diffusion zones, represented by the three light diffusion zones 221, 222, 223; wherein each light diffusion zone has a plural arrays of microstructures arranged on the surface thereof, and each array of microstructures is capable of changing the diopter of the corresponding light diffusion zone. By the arrays of microstructures distributed in the light diffusion zones 221, 222, 223, the light incident thereon can be diffused and shine upon the intended illuminating area 9 uniformally while the ineffective portion of light that points to the area outside the intended illuminating area 9 is collimated to shine upon the intended illuminating area 9. Thereby, not only the light efficiency of the light device can be enhanced, but also uniformity of the lighting device is improved.
Another such research is a luminaire disclosed in U.S. Pub. No. 20060139933, entitled “Reflector With Negative Focal Length”, as seen in FIG. 2. In FIG. 2, the top of the luminaire screen 20 is a reflector of single negative focal length 51, such that the cross section of the luminaire screen 20 is a concavity with a side screen 52 connecting to the edge of the reflector 51. By the luminaire screen 20 of FIG. 2, the upward-incident rays emitting from a light source 53 are first reflected to the side screen 52 by the reflector 51, and then are further reflected such that a plurality of discharging rays 54 are generated. It is noted that the discharging rays 54 are discharge out of the luminaire by large angles for reducing glare. In addition, the height of the luminaire can be reduced.
Yet, another such research is a light guide apparatus disclosed in U.S. Pub. No. 20050129357, entitled “Light Guide Apparatus for Enhancing Light Source Utilization Efficiency”, as seen in FIG. 3. In FIG. 3, a light guide apparatus for enhancing light source utilization efficiency 30 includes a light guide sheet 32, a light coupling structure 301 and a light emerging structure 302. The light coupling structure 301 is arranged on a surface of the light guide sheet 32 and opposite to a light source 31. The light emerging structure 302 is disposed on a surface of light guide sheet 32 that can be the same as, or opposite to that of the light coupling structure 301. Lights emitted by the light source 31 enters into the light guide sheet 32 via the light coupling structure 301 and evenly emitted to outer environment via said light emerging structure 302, thereby enhancing light source utilization efficiency
Although the means of the aforesaid researches are different from each other, they all can achieve the purposes of lighting efficacy enhancement and illuminance uniformity improvement. Nevertheless, it is still in need of an apparatus capable of preventing glare while achieving the purposes of lighting efficacy enhancement and illuminance uniformity improvement.